JPS6385060A - Manufacture of self-supporting ceramic composite material - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a novel method for manufacturing ceramic composite structures, and more particularly to a method for manufacturing ceramic composite structures, and more particularly for manufacturing polycrystalline materials containing oxidation reaction products from a parent metal. The present invention relates to an improvement in the method of manufacturing ceramic composite structures by growing into a permeable mass a filler containing crushed particles of polycrystalline material previously produced by the same general process.

BACKGROUND OF THE INVENTION There has been increasing interest in replacing metals with ceramics in recent years, due to the superiority of ceramics over metals with respect to several properties.

However, there are several known limitations and difficulties in making such replacements, such as size flexibility, difficulty in manufacturing articles with complex shapes, meeting the properties required for the end use, and cost. There is. Many of these limitations and difficulties are addressed in commonly assigned U.S. patent applications and the inventions described herein, in which ceramic materials, including composite materials, in a predetermined shape are not reliable. This problem has been overcome by an invention that provides a new method of manufacturing.

The following U.S. patent applications, assigned to the same assignee as the present applicant, disclose the preparation of self-supporting ceramic salts by oxidizing a parent metal to form a polycrystalline material consisting of the oxidation reaction products and optional metal components. A new method of manufacturing is described.

(A) No. 198, which is a continuation-in-part of U.S. Patent Application No. 591,392 filed March 16, 1984;
19, which is a continuation-in-part of U.S. Patent Application No. 776.964, dated September 17, 1985, which is a continuation-in-part of U.S. Pat.
U.S. Patent Application Section 818.943 dated January 15, 1986
issue.

(B) United States Patent Application Section 63 dated July 20, 1984.
June 25, 1985, which is a continuation in part of No. 2,636.
U.S. Patent Application Section 7, filed September 17, 1985, which is a continuation-in-part of U.S. Patent Application Section 747°788, dated September 17, 1985.
No. 76.965, a continuation-in-part application January 2, 1986
No. 70, U.S. Patent Application No. 822,999.

(c)1”) United States Patent Application Section 69 dated February 4, 1985
January 17, 1986, which is a continuation in part of No. 7,876.
No. 819.397, dated U.S. Patent Application No. 819.397.

The disclosures of each of the U.S. patent applications assigned to the same assignee and assignee mentioned above are hereby incorporated by reference.

As described in these U.S. patent applications, novel polycrystalline ceramic materials or polycrystalline ceramic composites are
It is produced by an oxidation reaction between a parent metal and a vapor phase oxidant, ie, a vaporized, usually gaseous material such as an oxidizing atmosphere.

This method is comprehensively described in the aforementioned US patent application (A). According to this comprehensive process, a parent metal, such as aluminum, is heated above its melting point to form a mass of molten parent metal that reacts to form an oxidation reaction product when it comes into contact with a gas-phase oxidant. Heated to a high temperature below the melting point of the substance. At this temperature, the oxidation reaction products, or at least a portion thereof, contact and extend between the molten parent metal mass and the oxidizing agent, and the molten parent metal absorbs the formed oxidation reaction products. through which it is sucked or transferred towards the oxidizer. When the transferred molten parent metal comes into contact with the oxidizing agent on the surface of the previously formed oxidation reaction product, it forms further oxidation reaction products. As this process continues, additional metal is thus transported through the τ-formed polycrystalline oxidation reaction product, thereby continuously growing a ceramic structure of interconnected crystallites. The ceramic salt thus obtained contains metallic components such as unoxidized components of the parent metal and vacancies. If the oxidation reaction product is an oxide, oxygen or a gas mixture containing oxygen (for example air) is suitable as the oxidizing agent, with air generally being preferred for obvious economic reasons. However, in all of the aforementioned U.S. patent applications and herein, oxidation is used in a broad sense, meaning that a metal donates electrons to or oxidizes an oxidizing agent, which may be one or more elements or compounds. It means sharing electrons with the agent. Therefore, as will be explained in detail later, elements or compounds other than oxygen may act as oxidizing agents.

In some cases, the presence of one or more dopants in the parent metal may be required to favorably influence or facilitate the growth of oxidation reaction products, and the dopant may be an alloy of the parent metal. given as an ingredient.

For example, when aluminum is used as the parent metal and air is used as the oxidizing agent, dopants such as magnesium and silicon, to name just two of the main types of dopant materials, are alloyed with the aluminum. , it is used as the parent metal. The resulting oxidation reaction product contains alumina, typically alpha-alumina.

The aforementioned U.S. Patent Application (B) discloses that suitable growth streaks as described above for parent metals requiring dopants are created by applying one or more dopant materials to the surface of the parent metal; Based on the discovery that when aluminum is the parent metal and air is the oxidizing agent, it is possible to eliminate the need to alloy the parent metal with dopant materials, such as metals such as magnesium, zinc, and silicon. Improvements are listed. This improvement makes it possible to use commercially available metals and alloys with or without suitably doped compositions. This discovery also shows that rather than ceramic growth occurring in a dispersed manner, ceramic growth can occur on one or more predetermined regions of the parent metal surface, thereby allowing ceramic growth to take place on one or more predetermined areas of the parent metal surface. It is also advantageous that by doping only or only a portion of one surface, the alumina production process can be applied more efficiently.

The aforementioned U.S. patent application (c) describes a novel ceramic composite structure that uses an oxidation reaction to produce a ceramic composite structure containing a substantially inert filler infiltrated with a polycrystalline ceramic matrix. A body and a method for its production are described. A parent metal disposed proximate to the mass of permeable filler material is heated, thereby forming a mass of molten parent metal that is reacted with a gas phase oxidant as described above to form an oxidation reaction product. Ru. As the oxidation reaction products grow and penetrate into the adjacent filler, the molten parent metal is drawn into the mass of the filler through the previously formed oxidation reaction products;
It reacts with the oxidizing agent to form additional oxidation reaction products on the surface of the previously formed oxidation reaction products as described above. The growth of the oxidation reaction product thus produced causes the filler to be penetrated by the oxidation reaction product, i.e. the filler is embedded in the oxidation reaction product, so that the filler is embedded in the matrix of the polycrystalline ceramic. A composite structure is formed.

Thus, the U.S. patent application, which is assigned to the same assignee as the above-mentioned applicant, is intended to achieve a desired goal that was previously considered to be difficult, if not impossible, to achieve by conventional ceramic processing methods. It has been described to produce oxidation reaction products that can be easily grown to dimensions and thicknesses of .

The present invention further improves the method for use in manufacturing ceramic composite products.

SUMMARY OF THE INVENTION The present invention is directed to a ceramic matrix containing a polycrystalline oxidation reaction product grown by oxidizing a molten parent metal in accordance with the above-identified commonly assigned U.S. patent application. The present invention relates to an improved method of manufacturing polycrystalline ceramic composite materials by filling with permeable masses or beds of filler. The filler material includes ground granules of polycrystalline material manufactured in accordance with the previously assigned commonly assigned U.S. patent application. By using a filler material that is a substantial replica (but not necessarily an exact replica) of the ceramic material produced prior to the composite product by a substantially identical process, as described in more detail later. As you do,
Improved ceramic forming behavior and improved morphology are obtained.

In the practice of the present invention, parent metal is heated in the presence of a vapor phase oxidant, thereby forming a mass of molten metal that contacts a bed of permeable filler material. Oxidation reaction products are formed by contact of molten metal with an oxidizing agent, and the process conditions are such that the molten metal is gradually drawn towards the oxidizing agent through the formed oxidation reaction product, thereby The oxidation reaction products are maintained to form continuously at the interface between the formed oxidation reaction products.

The heating step is carried out at a temperature above the melting point of the parent metal and below the melting point of the oxidation reaction product, and heating is continued for the time necessary to produce a polycrystalline ceramic mass of the desired size. Ru. The ceramic mass may contain one or more metal components, such as an unoxidized parent metal, and/or voids.

The improvements of the present invention are described in the Summary of the Invention section and described in detail in the aforementioned co-assigned U.S. patent application. It is based on the discovery that self-supporting ceramic composites can be obtained by using crushed agglomerates or granules of crystalline material as fillers. The polycrystalline material thus obtained is crushed and ground, and a mass of filler, preferably shaped as a permeable preform, is placed adjacent to a second mass of parent metal, and the assembly thus formed is Exposure to oxidation reaction processes. The reaction process involves filling at least a portion of the bed of filler with a polycrystalline oxidation reaction product formed from a second parent metal, sufficient to provide a ceramic composite structure of desired dimensions. continues over time.

More particularly, the second parent metal is applied to the permeable mass of the filler such that the formation of oxidation reaction products from the second parent metal occurs toward and into the mass of the filler. placed and oriented. The growth of the oxidation reaction products infiltrates the filler mass, thereby forming the desired ceramic composite structure. The filler material may be loosely arranged and bonded, characterized by interstices, pores, or intervening spaces, and the bed or mass of the filler material is permeable to the growth of gas phase oxidants and oxidation reaction products. have. As used herein, the term "filler" refers to a homogeneous composition or a heterogeneous composition of two or more materials. Thus, the filler may be mixed with one or more other fillers formed by conventional methods. Furthermore, the parent metal and oxidizing agent used in the process of producing the replicated filler material are substantially different in composition from the parent metal and oxidizing agent used in producing the final composite product. They may be the same or different.

The oxidation reaction products grow into the filler without disruption or displacement of the filler components, resulting in a relatively dense composite ceramic structure being formed without the use of high temperatures and pressures. Furthermore, the method of the present invention reduces or eliminates the need for chemical and physical compatibility, which are conditions commonly required when pressureless sintering methods are used to produce ceramic composite materials. be done.

The ceramic composite materials produced by the method of the invention have very favorable electrical, wear, thermal, and structural characteristics and, if desired, can be machined into products with various industrial applications. Processing such as machining, polishing, and grinding may be performed.

The following terms used in this specification have the following meanings.

"Ceramic" should not be interpreted narrowly as being limited to ceramic masses in the classical sense, i.e. consisting only of non-metallic and inorganic materials, but is derived from parent metals or A small or substantial amount (most typically in the range of about 1-40 vol. %, but higher amounts may be included) of one or more metal components generated from oxidizing agents and dopants. Refers to a mass that is predominantly ceramic in composition or predominant properties, even if it does contain it.

"Oxidation reaction product" means one or more metals in any oxidized state in which the metal has donated or shared electrons with other elements, compounds, or combinations thereof. Therefore, "oxidation reaction products" in this definition include oxygen, nitrogen, halogen, sulfur, phosphorus, arsenic, carbon, boron, selenium, tellurium, compounds and combinations thereof, such as methane, oxygen, ethane, propane, acetylene, Ethylene, propylene, and air, H2/ H20, CO/
The reaction of an oxidizing agent, such as a mixture such as CO2 (the latter two, namely H2/H20 and CO/C02, are important in reducing the oxygen activity of the environment) with one or more metals. Contains products.

"Oxidizing agent" refers to an oxidizing agent containing a specific gas or vapor,
Terms such as "vapor phase oxidant" mean that the identified gas or vapor is the only, primary, or at least Refers to an oxidizing agent that is an important means of oxidation. For example, the main component of air is nitrogen, but since oxygen is a stronger oxidizing agent than nitrogen, the oxygen component of air is the only oxidizing agent for the parent metal. Therefore, air belongs to the definition of an oxidizing agent as an "oxygen-containing gas" but does not fall under the definition of an oxidizing agent as a "nitrogen-containing gas."

One example of an oxidizing agent for "nitrogen-containing gas" herein is typically about 96 vol.
It is a "forming gas" containing VO1% hydrogen.

"Parent metal" means a metal, such as aluminum, that is a precursor for a polycrystalline oxidation reaction product, a relatively pure metal, a commercially available metal containing impurities or alloying components. , or an alloy whose main component is a metal precursor thereof.

Further, when a certain metal such as aluminum is called a parent metal, the metal must be interpreted according to this definition unless otherwise specified.

The invention will now be described in detail by way of example embodiments with reference to the accompanying drawings.

EXAMPLE In accordance with the present invention for producing a self-supporting ceramic composite, the parent metal is heated to a molten state in the presence of a vapor phase oxidizing agent, thereby causing the oxidation reaction products to penetrate into the bed or mass of the filler. is formed. The filler used is essentially crushed particles of polycrystalline material previously produced by the process described above. This filler is compatible with the oxidation reaction products that grow during the process to produce the final composite product, a compatibility that can clearly be attributed to the compatibility of similar materials under the process conditions. have. That is, there is a clear tendency for the reaction product to grow into its replica. Because of this trend, we have observed a higher growth effect, so that growth occurs somewhat more rapidly than in a substantially identical process without the replicated filler.

In addition, the inventors have filed a patent application no.
As described in No. 42, it has been observed that the morphology is improved and high quality replication of the parent metal pattern by the ceramic mass is achieved.

One factor that appears to contribute to such improved properties is the presence of a dopant material in close association with the filler. For example, when alumina as the oxidation reaction product is formed by the oxidation reaction of aluminum in air, the dopant material is used in conjunction or in combination with aluminum as the parent metal. The dopant or portions thereof are not consumed by the reaction system and therefore remain dispersed throughout some or all of the polycrystalline material. In such cases, the dopant material may be concentrated at the initial interface or outer surface of the polycrystalline material, or may be in close contact with the microstructure of the oxidation reaction product, or may be alloyed with the metallic components of the polycrystalline material. become. When the polycrystalline material is crushed for use as a filler, the dopant material incorporated as part of the filler acts as a useful dopant in the manufacture of the final composite product. For example, silicon is a useful dopant for the oxidation reaction of aluminum in air, and a significant proportion of the silicon alloys with the metallic phase of the polycrystalline material. Such polycrystalline materials, when used as fillers, contain dopants used in making alumina composites.

The ceramic mass produced as a filler source for the final composite product can be milled, e.g. by impact milling, roller milling, depending on the required particle size and the composition of the polycrystalline material.
It is crushed to the desired size by rotary crushing or other conventional methods.

The crushed material is sized and recovered for use as filler. For example, a ceramic lump is first crushed to zero using a show crusher, hammer mill, etc. 25-0, 51
It is preferable to crush the particles into relatively large particles of nch (0.64 to 1.3 mm), and then crush them into fine particles of 50 meshes or less using an impact mill or the like. The particles are sieved to obtain particles of desired size.

Preferred filler sizes range from 100 to 500 mesh or finer, depending on the ceramic composite to be produced and its end use.

As previously mentioned, the polycrystalline material that is formed includes metallic components such as unoxidized parent metals. The amount of metal varies over a wide range from 1 to 40 vol% and sometimes higher, depending largely on the degree of consumption (conversion) of the parent metal used during the process. Before using the polycrystalline material as a filler, it is preferred to separate at least a portion, especially a relatively large portion, of the metal from the oxidation reaction products. Such separation may be suitably carried out after the polycrystalline material has been crushed. Oxidation reaction products are generally more easily crushed than metals, so that the two components can optionally be partially separated by crushing and sieving.

Additionally, the unoxidized parent metal present in the filler is granular, and when used in forming the final product, undergoes an oxidation reaction to create voids in the ceramic matrix that correspond in size to the metal particles. Produces pores. Such pores dispersed in the ceramic matrix may or may not be desirable depending on the properties required of the composite material and its end use. When a high volume fraction of porosity is required in the final product, for example to increase the thermal insulation properties of composite materials, fillers with a substantial amount of unoxidized parent metal may be used. is advantageous. Simply forming a layered bed of filler containing (1) filler with a specific parent metal and (2) filler that is relatively pure (metal removed) or filler from other sources. , the pores contained therein can be confined to a portion of the composite material.

According to the present invention, the parent metal used in producing the filler material may be substantially the same as the parent metal used in producing the final ceramic composite product, and may be different from This is advantageous in that it allows the use of fillers that have some of the advantages mentioned above, but the oxidation reaction products are different in chemical composition from the oxidation reaction products of the final product. It differs in For example, according to this embodiment, an alumina ceramic mass, which is later used as a filler, is placed in an alumina-nitride ceramic matrix formed by air oxidation of aluminum as parent metal in a nitrogen atmosphere. , can be formed by an oxidation reaction of aluminum as a parent metal in an oxygen atmosphere.

In another embodiment, the filler used in manufacturing the final composite product is derived from a ceramic composite formed by an oxidation reaction process, crushed to size, and sieved. It is what was done. Fillers used in producing ceramic composite materials that are precursor fillers for the final product are selected to improve and enhance the properties of the final product. This means selecting a filler that differs in composition from the oxidation reaction product so that the resulting precursor filler consists of or contains two components closely joined together as a fine composite material. This is achieved by In producing a ceramic composite structure according to this embodiment, a first parent metal source and a permeable bed or mass of filler are provided in which the formation of oxidation reaction products is directed toward the bed of filler. oriented relative to each other so as to occur. the first parent metal source is heated in the presence of a gas phase oxidant;
This forms a mass of molten parent metal that reacts with the oxidizing agent in this temperature range, thereby forming an oxidation reaction product. The oxidation reaction product contacts and extends between the mass of molten parent metal and the oxidizer, thereby gradually directing the molten metal through the oxidation reaction product to the oxidizer and into the mass of filler. oxidation reaction products are continuously formed at the interface between the oxidizing agent and the previously formed oxidation reaction products. The reaction is continued for a period of time sufficient to fill at least a portion of the bed of packing material with polycrystalline material comprising the oxidation reaction product and optionally one or more metal components, such as the unoxidized parent metal. Ru. The obtained polycrystalline composite material is crushed to a certain size suitable for use as a second filler, and this second filler (different in composition from the first filler) is crushed. The permeable mass of the second filler material is oriented relative to the second parent metal source such that the formation of oxidation reaction products occurs toward and into the second mass of filler material. This oxidation reaction process is repeated as described above and continues for a sufficient period of time for the oxidation reaction products to penetrate at least a portion of the second filler mass, thereby forming the final ceramic composite product. be done.

The properties of the ceramic composite products of the present invention vary depending on factors such as parent metal type, filler composition, and oxidizing agent.

Typical properties required of these composite materials that can be adjusted include hardness, flexural strength, fracture toughness, and modulus of elasticity. Composite products generally include, but are not limited to, industrial, structural, and engineering ceramic masses for applications where electrical, wear, thermal, structural, or other properties are important. It may be adapted, for example, by machining, polishing, grinding, etc., for use as a commercial article, including (but not limited to)

Although the present invention is described herein in terms of a system in which aluminum or an aluminum alloy is used as the parent metal and alumina is the oxidation reaction product produced, this description is for illustrative purposes only. The present invention uses tin, silicon,
It should be noted that other systems in which other metals such as titanium, zirconium, etc. are used as parent metals are also applicable. Furthermore, the oxidation reaction products produced are oxides, nitrides, borides, carbides, etc. of the parent metal. In more detail regarding some of the process steps, a parent metal (which may be toped as described above) is formed into an ingot, billet, rod, plate, etc. as a precursor to the oxidation reaction product, and an inert Placed on the floor, crucible, or other refractory container.

This container and its contents are placed in a furnace that is supplied with a gas oxidizer. The container and contents are then heated to a temperature below the melting point of the oxidation reaction product and above the melting point of the parent metal. For example, for aluminum using air as the vapor phase oxidant, this temperature range is typically about 850 to 1
450°C, preferably about 900-1350°C. In this usable temperature range, a mass or pool of molten metal is formed which reacts when it comes into contact with an oxidizing agent to form a layer of oxidation reaction products. As the molten metal is continuously exposed to the oxidizing environment, it is gradually drawn into the previously formed oxidizing reaction products and through the oxidizing reaction products toward the oxidizing agent. The molten metal reacts upon contact with the oxidizing agent, thereby forming further oxidation reaction products, thus progressively increasing the thickness of the oxidation reaction products with the metal component optionally dispersed within the polycrystalline material. The reaction of the molten metal with the oxidant is continued until the oxidation reaction products grow to the desired limit or boundary.

In embodiments in which a ceramic composite is formed to act as a precursor filler, the permeable mass of parent metal and filler is such that the growth of oxidation reaction products as described above occurs toward the filler. This allows the oxidation reaction products growing on the filler or a portion thereof to penetrate and thereby be placed adjacent to each other and oriented relative to each other so as to be embedded in the oxidation reaction products. Thus, locating and orienting the parent metal and the filler relative to each other can be accomplished by simply placing a mass of the parent metal within a bed of granular filler, or by placing one or more masses of the parent metal in a bed of granular filler. This may be accomplished by placing it on or adjacent to a bed of filler or other assembly.

The assembly of fillers is arranged such that the oxidation reaction products penetrate at least a portion of the filler by growth. The filler may be, for example, a powder or other particulates, aggregates, refractory fibers, tubes, whiskers, balls, pieces or combinations thereof.

Further suitable fillers include alumina, magnesia, hafnia, zirconia, as described in the aforementioned co-assigned US patent application,
These include metal oxides, nitrides, or carbides such as silicon carbide, silicon nitride, zirconium nitride, titanium nitride, and the like.

The resulting polycrystalline material has pores that are a partial or almost complete replacement of the metallic phase, but the volume fraction of pores varies depending on temperature,
It is highly dependent on conditions such as time, type of parent metal, and concentration of dopants. Typically in such polycrystalline ceramic structures, the oxidation reaction product crystallites are interconnected in one or more dimensions, preferably three dimensions, and the metals are at least partially interconnected. is in a state of being

The polycrystalline ceramic material (or composite material, if manufactured) is then crushed and sized for use as a filler in manufacturing the final composite product. This particulate filler, which may be mixed with other fillers, is formed into a permeable bed, preferably a preform of a predetermined shape. The bed and the second parent metal are oriented relative to each other such that the formation of oxidation reaction products occurs toward and into the bed. The process steps described above are substantially repeated. The reaction process is continued for a sufficient period of time for the oxidation reaction products to penetrate at least a portion of the bed of filler material or the desired boundaries of the preform, thereby forming a ceramic composite.

One particularly useful method for practicing the present invention involves molding the filler material into a preform having a shape that corresponds to the desired geometry of the final composite product. The preforms can be produced by any of a wide range of ceramic mass forming methods (e.g. unidirectional pressing, isostatic pressing, slip casting, precipitation casting, tape casting, injection molding, filament winding for fibrous materials, etc.) depending on the properties of the filler. May be done.

Various organic or inorganic binders that first bind the particles together prior to infiltration by light sintering or that do not adversely affect the composite manufacturing process or introduce undesirable by-products in the finished material. This can be done by using . The preform must be manufactured to have sufficient shape retention and wet strength to permit penetration of oxidation reaction products, and must have a
It is preferred to have a porosity of 90vol%, preferably about 25-50vol%. Mixtures of fillers of various sizes may also be used. The preform is then brought into contact with molten parent metal at one or more of its surfaces for a period of time sufficient to cause complete growth to the surface boundaries and penetration into the preform.

Oxidation reaction products grow beyond the barrier means, as described in U.S. Patent Application No. 861.024, filed May 1986 and assigned to the same assignee. Barrier means may be used in conjunction with the filler or filler preform to prevent this. Suitable barrier means maintain some degree of integrity under the process conditions of the present invention, do not evaporate, are permeable to the gas phase oxidant, and yet prevent further oxidation reaction products from evaporating. It may be any material, compound, element, composition, etc. that can locally prevent, stop, interfere with, or inhibit continued growth. Calcium sulfide (Plaster o
f' Paris), calcium silicate, Portland cement, and mixtures thereof, which are typically applied as a slurry or paste to the surface of the filler. These barrier means may also include suitable combustible or volatile materials that dissipate when heated, or include materials that decompose when heated to increase the porosity and permeability of the barrier means. It's okay to stay. Additionally, the barrier means may include suitable refractory particles to reduce shrinkage and cracking that may occur during processing.

Particularly preferred are particles that have a coefficient of thermal expansion that is substantially the same as that of the bed of filler or preform. For example, if the preform comprises alumina and the resulting ceramic comprises alumina, the barrier means preferably has a
It may be mixed with alumina particles having a mesh size of 1000 (or even finer). Other suitable barrier means include refractory ceramic or metal containers that are open at at least one end to allow the vapor phase oxidant to penetrate the bed of filler material and contact the molten parent metal.

As a result of the use of preforms, especially in combination with barrier means, a net shape is obtained, which allows expensive final machining or grinding steps to be reduced or eliminated.

In yet another embodiment of the present invention, oxidation can be achieved by adding a dopant material in conjunction with the parent metal, as described in the aforementioned co-assigned U.S. patent application. The reaction is favorably influenced. The functionality of a dopant material depends on many factors other than the dopant material itself. Such factors include, for example, the particular parent metal, the required end product, the particular combination of dopants when two or more dopants are used, and the external effects in combination with alloyed dopants. The applicable dopant use, dopant concentration, oxidation environment, process conditions, etc.

A dopant used in conjunction with a parent metal may (1) be provided as an alloying component of the parent metal, (2) be applied to at least a portion of the surface of the parent metal, and (3) be a filler. It may be applied to the floor or preform or a part thereof, or any combination of two or more of these methods (1) to (3) may be employed. For example, alloyed dopants may be used in combination with externally applied dopants. In case (3) above, where the dopant is applied to the bed of filler or to the preform, the dopant is applied as a coating or in particulate form to part or the entire mass of the preform (at least to the parent part of the preform). This may be achieved in any suitable manner, such as by dispersing the redopant throughout the area (preferably including the portion adjacent to the metal). Applying dopants to the preform also
internal pores, interstices, which make the preform permeable;
This may be accomplished by applying one or more layers of dopant material to and within the preform containing channels, interior spaces, etc. A suitable conventional method of applying any dopant is simply to immerse the entire bed of filler material in a liquid (eg, solution) of the dopant material.

As previously mentioned, dopants may be incorporated into the fillers used in manufacturing the final composite product. A second source of dopant may also be provided by placing a rigid mass of dopant between and in contact with at least a portion of the surface of the parent metal and the preform. For example, a thin sheet of silicon-containing glass, which is a useful dopant for the oxidation of aluminum as a parent metal, may be placed on the surface of the parent metal. When the parent metal aluminum (which may be internally doped with Mg) on which a silicon-containing glass is fused is melted in an oxidizing environment (e.g., in the case of aluminum, the
℃, preferably about 900-1350 degrees Celsius), the growth of polycrystalline ceramic material into the permeable preform begins. When the dopant is applied externally to at least a portion of the surface of the parent metal, the polycrystalline oxidation reaction product extends substantially beyond the dopant layer (i.e., beyond the thickness of the applied dopant layer). ) grown in a permeable preform. In either case, one or more dopants may be applied externally to the surface of the parent metal or to the permeable preform. Additionally, dopants alloyed within the parent metal or dopants applied externally to the parent metal may be assisted by dopants applied to the preform. Thus, any deficiency in the concentration of dopant alloyed within the parent metal or applied externally to the parent metal is compensated for by the dopant applied to the preform, and vice versa. Even if the concentration of dopants is low, this can be compensated for by dopants alloyed into the parent metal or applied externally to the parent metal.

Useful dopants for aluminum as the parent metal, especially when air is used as the oxidizing agent, include magnesium, zinc, etc., in combination with each other or with other dopants described below. and silicon. These metals, or a suitable source thereof, may be alloyed into the aluminum-based parent metal at a concentration of about 0.1 to 10 vt%, each based on the total weight of the resulting doped metal. Concentrations in this range are believed to initiate ceramic growth, improve metal transport, and favorably influence the growth morphology of the resulting oxidation reaction products. The concentration range for any one dopant depends on factors such as dopant combination and process temperature.

Other dopants that are effective in promoting the growth of polycrystalline oxidation reaction products for aluminum-based parent metals include germanium, tin, especially when used in combination with magnesium and zinc. and lead. One or more of these other dopants or a suitable source thereof each accounts for about 0.5 of the total alloy.
Although alloyed in the parent metal system of aluminum at concentrations of ˜15 wt %, even more favorable growth behavior and morphology are obtained at dopant concentrations ranging from about 1 to 10 vt % of the total parent metal alloy. Lead as a dopant is generally alloyed into an aluminum-based parent metal at temperatures of at least 1000°C to compensate for the low solubility of lead in aluminum, but other alloys such as tin The addition of elements generally increases the solubility of lead, thereby allowing alloying elements to be added at relatively low temperatures.

As mentioned above, one or more dopants may be used depending on the circumstances. For example, when the parent metal is aluminum and the oxidizing agent is air, particularly useful dopant combinations include (a) magnesium and silicon, or (b) magnesium, zinc, and silicon. In such instances, the preferred concentration of magnesium is about 0.1-3v
t%, with the preferred concentration of zinc being about 1-6 wt.
%, with the preferred concentration of silicon being about 1-10v
It is in the range of t%.

Other examples of useful dopant materials when the parent metal is aluminum include sodium, lithium, calcium,
These include boron, phosphorus, and yttrium, each of which may be used alone or in combination with one or other dopants, depending on the oxidizing agent and process conditions. Sodium and lithium are present in very small amounts, typically about 100-2
00 ppm, each alone or in combination with each other or with other dopants. Rare earth elements such as cerium, lanthanum, praseodymium, neodymium, and samarium are also useful dopants, especially when used in combination with other dopants. As mentioned above, there is no need to alloy the dopant material into the parent metal. For example, by selectively applying one or more dopant materials as a thin layer to all or a portion of the parent metal surface, the ceramic may be grown locally over the parent metal surface or a portion thereof. and polycrystalline ceramics can be grown in predetermined areas of the permeable bed or preform. Thus, the growth of polycrystalline ceramics can be controlled by localized placement of dopant materials on the surface of the parent metal. The coating or layer of dopant applied is small compared to the thickness of the parent metal mass, and the oxidation reaction products that grow into the permeable bed or preform substantially extend beyond the layer of dopant, i.e. extending beyond the thickness of the dopant layer. The layer containing the dopant material is coated,
Dipping, silk-screening, vapor deposition, or other methods of applying the dopant material in liquid or paste form, or thermal spraying, or simply applying a layer of solid particulate dopant or a solid thin sheet or film of dopant to the parent metal. It may be applied by a method such as placing it on the surface of. Dopant materials may include organic or inorganic binders, vehicles, solvents, or thickeners. More particularly, the dopant material is applied as a powder to the surface of the parent metal or dispersed in at least a portion of the filler. One particularly preferred method of applying the dopant to the surface of the parent metal uses a liquid dispersion of the dopant dispersed in a mixture of water and an organic binder that is sprayed onto the surface of the parent metal to obtain an adhesive coating. This method facilitates handling of the doped parent metal prior to processing.

Externally used dopants are generally applied as a uniform coating to a portion of the surface of the parent metal.

The amount of dopant may have a wide range of values compared to the amount of parent metal to which it is applied; if the parent metal is aluminum, upper and lower dopant limits can be determined experimentally. There wasn't. If silicon is used in the form of silicon dioxide applied externally as a dopant to the parent metal, e.g. based on aluminium, and air or oxygen is used as the oxidizing agent, it has a source of magnesium or zinc. When 0.00003 g of silicon per gram of parent metal or about 0.0001 g of silicon per cJ of exposed surface of the parent metal is used with the second dopant, polycrystalline ceramic growth phenomena occur. Also, about 0.00 per gram of parent metal to be oxidized
If MgO is used as a dopant in an amount of 0.08 g Mg or more and 0.003 g Mg or more per 1 c of the surface of the parent metal to which MgO is applied, air or oxygen can be used as an oxidizing agent. It has been found that ceramic structures can be formed from silicon-containing aluminum parent metals. Increasing the amount of dopant material to a certain extent reduces the reaction time required to produce the ceramic composite, but this is dependent on factors such as dopant type, parent metal, and reaction conditions.

When the parent metal is aluminum internally doped with magnesium and the oxidizing medium is air or oxygen,
Magnesium was found to be at least partially oxidized than the alloy at temperatures of about 820-950°C. In such cases of parent metal aluminum systems doped with magnesium, the magnesium forms a magnesium oxide or magnesium aluminate spinel phase at the surface of the molten aluminum alloy, and during the alumina growth process such magnesium compounds primarily grow. The initial oxide surface of the parent metal alloy in the ceramic structure (II!I
] remains on the oxidation initiation surface). Therefore, in such magnesium-doped parent metal aluminum systems, the alumina-based structure is formed separately from the relatively thin layer of magnesium aluminate spinel present at the oxidation initiation surface.

If necessary, this oxidation initiation surface is easily removed by grinding, machining, polishing or grid blasting the polycrystalline ceramic article before the milling process.

The following examples illustrate the method of the invention and the results of its implementation.

Example 1 The filler for the grown ceramic composite of the present invention is obtained by crushing and pulverizing a ceramic mass formed according to the method described in the above-mentioned commonly assigned U.S. patent application. was formed by In detail, commercially available aluminum alloys (Alloy 38, which will be further described below)
Bars of slightly lower purity (0.1) are converted to ceramic by being oxidized in air at 1080°C for 72 hours, a time sufficient to fully react the aluminum parent metal. It was done. During this process, the aluminum alloy rod is mixed with alumina particles (Norton E-
The oxidation occurred from the exposed surface of the metal towards the air atmosphere. After cooling to ambient temperature, the grown ceramic pieces are separated from the bed particles that loosely adhere to them, separated from the thin oxide skin that has grown on the unexposed metal surfaces, and separated from any residual metal remaining in the bed. It was done.

These grown ceramic pieces were converted into particles for use as composite fillers by a combination of crushing and milling. Specifically, the ceramic pieces were first crushed in a show crusher to a maximum particle size of 0.25 inches (0.64 cm) and then further reduced in particle size in a dry vibratory mill for 24 hours. The resulting powder was sieved to separate the -100/+200 mesh powder used in composite filler applications.

As a comparison material, fused alumina particles (NorLon 38 Arundu
m) is crushed in a roll crusher and ground in a dry ball mill to separate a -100/+200 mesh powder, i.e. a powder with particle size identical to that selected for the grown and crushed filler. It was carefully sieved.

Ceramic composite masses were formed using these two types of fillers for comparison purposes. Two high alumina refractory saucers are coated with a layer of wollastonite, a material that acts as a barrier to the oxidation reaction process. 5inch(1,
It was first filled to a depth of 3 cm). Next, a 9X2X0.5 inch (2
3X5. IXl, 3cIll) rods were placed on the wollastonite layer in each saucer. In addition to aluminum, this aluminum alloy nominally contains about 7.5 to 9.5 wt%St,
3.0-4°OvL%Cu, ~2. 9wt%Zn
, ~l, Ovt%Fe, ~0.5vt%Ml, ~
0. 5vt%N11~o.

The other samples of 380.1 alloy used in this test contained approximately 0.17 to 0.18 wt% Mg, whereas the other samples of 380.1 alloy used in this test contained approximately 0.17 to 0.18 wt% Mg.
was found to contain. This is an important modification from the nominal specifications since magnesium is an excellent dopant or promoter of oxidation reactions. Next, the aluminum alloy rod had a small number of filler particles (approximately 0 and 51 nch (1, 30 nch) on all sides except the bottom surface).
surrounded to a depth of m).

In this case, a grown and crushed filler was used for one pan, and a molten alumina filler was used for the other pan.

The refractory saucer filled as described above was then placed in an air oven, heated to 1000°C over 5 hours, and then heated to that temperature for 6 hours.
It was heated to a temperature of 1000° C. using a heating cycle of 0 hours hold and 5 hours furnace cooling. The grown ceramic composite was then separated from the barrier and remaining bed material, and any particles loosely adhered thereto were removed by light grid blasting.

Analysis of the weight gain data, determined for the two samples as the change in the weight of the refractory saucer and its contents divided by the initial weight of the aluminum alloy, revealed that approximately equal amounts of reaction occurred in each filler. I understand that it is. Specifically, the oxygen increase was 59% for the grown and crushed filler and 56% for the melted alumina filler. However, as can be seen from the comparison of Figures 1A and 1B, the growth into the grown and fractured filler is fairly uniform, which is an important processing advantage.

It can be seen that the mechanical properties determined for the specimens obtained from the two types of materials are significantly different from each other, as summarized in Table 1 below. In this table, the elastic modulus was determined by the sonic method, the fracture toughness was determined by a conventional chevron notch test, and the modulus of rupture was determined by a four-point bending test.

The data presented in this table show that the material formed by growth into a grown and fractured filler is clearly superior in terms of mechanical properties.

Table 1 Filling material properties Growth and crushing Molten alumina hardness*
84 71 elastic modulus
316 202 (GPa) Fracture toughness 4.67 2.74 (M P
a-m floors) Modulus of rupture 256 67 (MPa) *...Rockwell A hardness Example 2 The growth of the final ceramic composite lump is 380 in Example 1
．． The Example 10 procedure was repeated as described above, except that 99.7% pure aluminum was used as the parent metal instead of the 1 alloy. In this case, growth occurs easily into the grown and crushed filler, and as measured as in Example 1, 65
% weight gain and a very uniform growth pattern as shown in Figure 2A. On the other hand, no ceramic growth occurs in the melted alumina filler, and secondary
For this specimen shown in Figure B, the weight gain is negative, indicating that less volatile components were lost than the saucer and bed materials. Thus, in this example, the growth of the ceramic matrix into the grown and crushed filler was clearly preferable to the growth into the conventional smelted alumina particles. The mechanical properties of the composite material obtained by growing into the grown and crushed filler are very similar to those of the material produced using the same filler produced in Example 1. The values were similar or even higher.

Although the present invention has been described in detail with respect to specific embodiments above, the present invention is not limited to such embodiments, and various other embodiments are possible within the scope of the present invention. This will be clear to those skilled in the art.

[Brief Description of the Drawings] Figure 1A shows the growth form that appears outside of a specimen prepared by oxidizing the parent metal of aluminum alloy 380.1 within the bed of grown and crushed alumina particles. This is an exterior photo. FIG. 1B is an external photograph showing the growth morphology appearing outside of a specimen obtained by oxidizing the parent metal of aluminum alloy 380.1 in a bed of ingot alumina particles. FIG. 2A is an exterior photograph showing the growth morphology appearing outside of a specimen obtained by oxidizing parent metal of 99.796 pure aluminum into a bed of grown and crushed alumina particles. Figure 2B shows 99.7% of the melted alumina particles entering the bed.
3 is an external photograph showing the growth form that appeared on the outside of a specimen obtained by oxidizing a parent metal of % pure aluminum.

Claims (3)

[Claims] (1) A method for producing a self-supporting ceramic composite material comprising a ceramic matrix obtained as an oxidation reaction product of a parent metal with a gas-phase oxidizing agent, and a filler filled with the ceramic matrix, comprising: (a) ) heating a first parent metal source in the presence of a vapor phase oxidizing agent to form a mass of molten parent metal, reacting the molten parent metal with the oxidizing agent at a temperature, thereby forming an oxidation reaction product in contact with and extending between the mass of the molten parent metal and the oxidizing agent; (b) the oxidation reaction product is formed with the oxidizing agent first; oxidation reaction products, so that they are continuously formed at the interface between the oxidation reaction products and the
(c) maintaining said temperature and gradually drawing molten metal through said oxidation reaction product and toward said oxidizing agent; (d) reducing the polycrystalline material to a granular size for use as a filler and permeable mass of the granular filler; (e) forming a second parent metal source and the mass of particulate filler such that formation of an oxidation reaction product occurs toward and into the mass of particulate filler; (f) said step (a) for said second parent metal source;
, (b), and (c); and (g) for a sufficient time that the oxidation reaction product fills at least a portion of the mass of particulate filler, thereby forming the ceramic composite material. and continuing the reaction throughout. (2) A method for producing a self-supporting ceramic composite material comprising a ceramic matrix obtained as an oxidation reaction product of a parent metal with a gas-phase oxidizing agent, and a filler filled with the ceramic matrix, comprising: (a) ) heating a first source of parent metal aluminum in the presence of air as an oxidizing agent and in combination with at least one dopant material to form a mass of molten parent metal; The oxidizing agent is reacted with the oxidizing agent at a temperature of 850 to 1450° C., so that alumina is produced as an oxidation reaction product in contact with and extending between the molten parent metal mass and the oxidizing agent. (b) such that an oxidation reaction product is continuously formed at the interface between the oxidizing agent and the previously formed oxidation reaction product;
(c) maintaining said temperature and gradually drawing molten metal through said oxidation reaction product and toward said oxidizing agent; and (c) said oxidation reaction product and optionally one or more metal components. (d) reducing the polycrystalline material to a granular size for use as a filler and allowing penetration of the granular filler; forming a preform; (e) orienting a second parent metallic aluminum source and the preform relative to each other such that formation of oxidation reaction products occurs toward and into the preform; (f) said step (a) for said second parent metal source.
, (b), and (c); and (g) for a sufficient time that the oxidation reaction product fills the preform, thereby forming the ceramic composite material having the shape of the preform. and continuing the reaction throughout. (3) A method for producing a self-supporting ceramic composite material comprising a ceramic matrix obtained as an oxidation reaction product of a parent metal with a gas-phase oxidizing agent, and a filler filled with the ceramic matrix, comprising: (a) ) a first parent metal source and a permeable mass of the first filler such that the formation of the oxidation reaction product occurs toward and into the permeable mass of the first filler; (b) heating said first source of parent metal in the presence of a vapor phase oxidant to form a mass of molten parent metal, and bringing said molten parent metal to a temperature. (c) reacting with the oxidizing agent to form an oxidation reaction product in contact with and extending between the lump of the molten parent metal and the oxidizing agent; such that a reaction product is continuously formed at the interface between the oxidizing agent and the previously formed oxidation reaction product;
(d) maintaining said temperature to gradually draw molten metal through said oxidation reaction product toward said oxidizing agent and into said first mass of particulate filler; continuing the reaction for a time sufficient to fill at least a portion of the first particulate filler mass with a polycrystalline ceramic material comprising one filler and optionally one or more metal components; (e) reducing the polycrystalline ceramic material to a granular size suitable for use as a second filler to form a permeable mass of the second filler; f) orienting a second parent metal source and said second mass of filler relative to each other such that formation of oxidation reaction products occurs toward and into said mass of particulate filler; (g) said step (a) for said second parent metal source;
, (b), (c), and (d); and (h) an oxidation reaction product fills at least a portion of the second filler mass, thereby forming the ceramic composite material. and continuing the reaction for a sufficient period of time to provide a self-supporting ceramic composite material.